The invention relates to a process for producing a wood sheet from another wood sheet as starting material. Said wood sheets may be veneers.
The manufacture of veneers is a production technique for the manufacture of decorative, high-quality surface materials made from real wood. In the conventional manufacture, logs are decorticated or de-barked. Said logs are sawn into halves, thirds, quarters or other parts of a log (so called “flitches”). The flitches are mostly subsequently watered for several days at an increased temperature in order to prepare them for the subsequent cutting to veneer, the so-called slicing. Dependent on the cutting process, sliced veneer (horizontal or vertical slicing), peeled veneer (rotary slicing) or staylog (eccentrical rotary slicing) may be produced.
The obtained raw veneer, which typically has a thicknesses of from about 0.45 mm to 2.5 mm, preferably of from 0.45 mm to 0.8 mm, mostly is dried within some minutes, preferably at temperatures above 100° C. In case of strong corrugation, or “buckling,” said veneer is additionally subjected to a pressing step. Subsequently, the dried raw veneer is cut to size and is sorted according to qualities. For said cutting to size, high material losses have to be accepted, which can be up to 60%. Material loss with the manufacture of a veneer is intensified by the fact that the starting material “wood” respectively “tree” is a natural product. Inclusions, limb rudiments and imperfections in the log are often unrecognizable, and may therefore result in defects in the raw veneer that frequently cannot be accepted for its further processing. All this may result in up to 85% material waste from the raw material log up to the final acceptable cut-to-size veneer.
The above described process steps are comprised by the so-called “European method” or “North American method” for the manufacture of veneers.
In another technical process, the so-called “Asian method”, said raw veneer is obtained in a thickness of approximately from 0.1 mm to 0.8 mm. After the optional clipping of the edges (lengthwise), the still wet sheets of veneer are applied onto a substrate by means of gluing. Mostly the substrate is plywood. The customers buy the “fancy plywood” and cut out the part of the panel that they need. This results in low yields, as the needed sizes do not necessarily match the size of the plywood panel. Said “Asian method” requires an integrated process. The veneer after the slicing of the flitch/block has a high moisture content above the fiber saturation point of the wood. Leaving the sheet laying for a little while creates mold and deterioration of the veneers making them unusable. No storage or transportation over longer distances is possible. Only once the veneer is pressed on the substrate, the product can be transported/handled. The value of the substrate is considerably lower than the veneer itself. Thereby, a veneer product can be economically transported significantly farther than a fancy plywood product. This is particularly important with increasing transport cost.
So-called reconstituted veneers are also known. In the manufacturing process thereof, it is aspired to achieve a repeatable decorative property, a constant quality and a dimensional accuracy in order to be able to better predict the characteristics of the final product veneer. Conventionally manufactured veneers such as peeled veneers, optionally after a pretreatment such as dyeing or baking of structures, are glued to each other, and the so obtained material is subsequently re-sliced. Thereby, a veneer surface can be created having a mostly predetermined surface structure. Typically, soft wood species have to be used, otherwise the cutting process may be disadvantageously affected or even does not work at all. Due to the use of soft wood, the scratch resistance of the produced veneer may be impaired.
In another conventional process for the manufacture of reconstituted veneer, sliced or peeled hardwood veneer is laminated to a block and is re-sliced, wherein the block has a moisture content below the fiber saturation point. Since dried veneer is used, the resulting sheet is usually brittle and thus difficult to handle. Processing is limited with regard to parameters such as width and length of the veneer, since dry wood can be sliced only within narrow parameters. Typically, such a veneer needs to be glued on a substrate before further processing. This adds costs to the manufacturing process.
Specific manufacturing processes for a veneer are e.g. disclosed in the following documents of the prior art:
EP 1 275 481 discloses a process for the manufacture of wood veneer, wherein printed wood sheets having a moisture content of approximately 4% are glued together to form a flitch. After the glue hardening, the resulting flitch is sliced.
U.S. Pat. Nos. 3,977,449 and 3,878,016 disclose a process for the manufacture of wood veneer wherein individual flitches are glued to each other by means of an adhesive to form a composite flitch. The composite flitch is subsequently sliced to form a wood sheet such as a veneer which is glued to a substrate by means of an adhesive. Throughout, all process steps are carried out while the wood is maintained at a moisture content at or above the fiber saturation point of the wood. Also the moisture content of the obtained veneer is kept at or above the fiber saturation point prior to the gluing on a substrate.
U.S. Pat. No. 3,969,558 discloses the gluing of short pieces of a wooden beam to each other, which subsequently can be sliced. For the gluing, adhesives such as epoxy resin, phenolic resin and resorcinol resin are suggested. During the whole process, the moisture content of the wood is permanently held on or above the fiber saturation point. The produced veneer, which has a moisture content above the fiber saturation point of the wood is overlaid and glued onto a substrate.
U.S. Pat. No. 3,977,933 discloses a process for the manufacture of a veneer and fancy plywood therefrom. Herein, composite flitches made up of glued smaller flitches or sliced large veneer may be sliced to veneer, which subsequently is glued onto a substrate. All steps may be carried out at or above the fiber saturation point.
U.S. Pat. No. 5,143,792 discloses a method of forming a flitch from sheets of veneer, wherein the flitch is subjected to cooking in water before slicing.
U.S. Pat. No. 3,897,581 discloses a process for the manufacture of wood veneer, wherein wet wood pieces having a water content of more than 25% are glued to each other using a liquid anhydrous isocyanate-containing adhesive. The thus bonded wood can be cut with a rotary lathe, a slicer or a disc saw.
U.S. Pat. No. 4,293,362 discloses a process, wherein a composite consisting of glued wood sheets is cut into pieces. The pieces are glued on a backing member.
U.S. Pat. No. 4,388,133 discloses a method for producing a veneer, wherein material veneers are joined through a binder to form a flitch. Subsequently, the flitch is sliced to form an artificial wood veneer.
JP 10086107 discloses reconstituted veneer for plywood, wherein a general veneer for plywood is bonded to one another with a foam adhesive to make a log-like formed body. Said body is formed in a veneer in the same process as an ordinary log.
FR 2591933 discloses a process for the manufacture of a reconstituted veneer in a thickness of about 2 mm.
JP 3083632 discloses a structure of laminated veneers and aluminum sheets.
JP 2003276002 discloses an artificial veneer obtained from a laminated flitch by slicing.
CN 101357470 discloses a method for manufacturing reconstituted wood.
CN 101294442 discloses a method, wherein a plurality of wood single plates, which is integrated into a blank, is cut.
EP 1 688 228 discloses a process for the manufacture of wood veneer, wherein board-like plane pieces of wood are glued to each other to form a beam-like block of wood. Prior to the slicing, said block is watered. The obtained veneer is dried until the moisture content of the wood is below the fiber saturation point.